This invention relates to an aqueous composition suitable for use when dry as an improved elastomeric coating, caulk, sealant or pressure sensitive adhesive, a method for preparing an aqueous emulsion polymer suitable for use as an improved elastomeric coating, caulk, sealant or pressure sensitive adhesive, and a methods for providing an improved elastomeric coating, caulk or sealant, or pressure sensitive adhesive. More particularly this invention relates to an aqueous composition suitable for use when dry as an improved elastomeric coating, caulk, sealant or pressure sensitive adhesive including a predominantly acrylic aqueous emulsion polymer, the polymer having a glass transition temperature (Tg) from xe2x88x9290xc2x0 C. to 20xc2x0 C., the polymer formed by the free radical polymerization of at least one ethylenically unsaturated nonionic acrylic monomer and 0.5-5%, by weight based on the total weight of the polymer, ethylenically unsaturated carboxylic acid monomer, until 90-99.7% of the monomers by weight, based on the total weight of the polymer, has been converted to polymer; and the subsequent polymerization at least half, by weight, of the remaining monomer to polymer in the presence of 0.1-1.0%, by weight based on the total weight of the polymer, t-amyl hydroperoxide.
The present invention serves to provide an aqueous composition suitable for use when dry as an improved elastomeric coating, caulk, or sealant so as to retain its integrity without cracking under stress even at temperatures below 0 C. Elastomeric coatings, caulks, and sealants are frequently applied to buildings and other constructions subjected to outdoor temperature extremes and desirably retain their integrity under such conditions. Also, the present serves to provide an aqueous composition suitable for use when dry as an improved pressure sensitive adhesive having improved tack which may be desirable in itself or, alternatively, provide the basis for enhancement of other adhesive properties such as peel or shear strength with retention of useful levels of tack.
U.S. Pat. No. 5,540,987 discloses emulsion polymers having low residual formaldehyde and providing saturated cellulosic webs having improved. tensile strength. The polymers are formed by the use of an hydrophobic hydroperoxide and ascorbic acid initiator throughout the course of the reaction.
The problem faced by the inventors is the provision of an aqueous composition suitable for use when dry as an improved elastomeric coating, caulk, sealant or pressure sensitive adhesive. Unexpectedly, the inventors found that the use of t-amyl hydroperoxide in the last stages of the polymerization was sufficient to provide polymers which led improved elastomeric coating, caulk, sealant or pressure sensitive adhesives.
In a first aspect of the present invention there is provided an aqueous composition suitable for use when dry as an improved elastomeric coating, caulk, sealant or pressure sensitive adhesive including a predominantly acrylic aqueous emulsion polymer, the polymer having a glass transition temperature (Tg) from xe2x88x9290xc2x0 C. to 20xc2x0 C., formed by the free radical polymerization of at least one ethylenically unsaturated nonionic acrylic monomer and 0.5-5%, by weight based on the total weight of the polymer, ethylenically unsaturated carboxylic acid monomer until 90-99.7% of the monomers by weight, based on the total weight of the polymer, has been converted to polymer and subsequently at least half of the remaining monomer is converted to polymer in the presence of 0.1-1.0%, by weight based on the total weight of the polymer, t-amyl hydroperoxide.
In a second aspect of the present invention there is provided a method for preparing an aqueous emulsion polymer suitable for use in an improved elastomeric coating, caulk, sealant or pressure sensitive adhesive including forming a predominantly acrylic aqueous emulsion polymer, the polymer having a glass transition temperature (Tg) from xe2x88x9290xc2x0 C. to 20xc2x0 C., by the free radical polymerization of at least one ethylenically unsaturated nonionic acrylic monomer and 0.5-5%, by weight based on the total weight of the polymer, ethylenically unsaturated carboxylic acid monomer until 90-99.7% of the monomers by weight, based on the total weight of the polymer, has been converted to polymer; and subsequently polymerizing at least half of the remaining monomer to polymer in the presence of 0.1-1.0%, by weight based on the total weight of said polymer, t-amyl hydroperoxide.
In a third aspect of the present invention there is provided a method for coating a substrate with an aqueous composition to provide an elastomeric coating on a substrate. In a fourth aspect of the present invention there is provided a method for applying an aqueous caulk or sealant composition to a substrate. In a fifth aspect of the present invention there is provided a method for providing a pressure sensitive adhesive on a substrate.
This invention relates to an aqueous composition suitable for use when dry as an elastomeric coating having improved low temperature elongation including a predominantly acrylic aqueous emulsion polymer, the polymer having a glass transition temperature (Tg) from xe2x88x9290xc2x0 C. to 20xc2x0 C., formed by the free radical polymerization of at least one ethylenically unsaturated nonionic acrylic monomer and 0.5-5%, by weight based on the total weight of the polymer, ethylenically unsaturated carboxylic acid monomer until 90-99.7% of the monomers by weight, based on the total weight of the polymer, has been converted to polymer and subsequently at least half of the remaining monomer is converted to polymer in the presence of 0.1-1.0%, by weight based on the total weight of the polymer, t-amyl hydroperoxide.
The predominantly acrylic aqueous emulsion polymer contains at least one copolymerized ethylenically unsaturated nonionic acrylic monomer. By xe2x80x9cpredominantly acrylicxe2x80x9d herein is meant that the polymer contains greater than 50%, by weight, copolymerized units deriving from (meth)acrylic monomers such as, for example, (meth)acrylate esters, (meth)acrylamides, (meth)acrylonitrile, and (meth)acrylic acid. The use of the term xe2x80x9c(meth)xe2x80x9d followed by another term such as acrylate or acrylamide, as used throughout the disclosure, refers to both acrylates or acrylamides and methacrylates and methacrylamides, respectively.
By xe2x80x9cnonionic monomerxe2x80x9d herein is meant that the copolymerized monomer residue does not bear an ionic charge between pH=1-14.
The ethylenically unsaturated nonionic acrylic monomers include, for example, (meth)acrylic ester monomers including methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, lauryl acrylate, methyl methacrylate, butyl methacrylate, isodecyl methacrylate, lauryl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate. Other ethylenically unsaturated nonionic monomers which may be incorporated into the polymer with the proviso that the polymer must be predominantly acrylic in composition include, for example, styrene and substituted styrenes; butadiene; vinyl acetate, vinyl butyrate and other vinyl esters; and vinyl monomers such as vinyl chloride, vinylidene chloride. Preferred are all-acrylic, styrene/acrylic, and vinyl acertate/acrylic polymers.
The emulsion polymer contains from 0.5% to 5%, by weight based on total monomer weight, of a copolymerized monoethylenically-unsaturated carboxylic acid monomer, based on the weight of the polymer, such as, for example, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, monomethyl itaconate, monomethyl fumarate, monobutyl fumarate, and maleic anhydride.
The emulsion polymer used in this invention may contain from 0% to 1%, by weight based on monomer weight, copolymerized multi-ethylenically unsaturated monomers such as, for example, allyl methacrylate, diallyl phthalate, 1,4-butylene glycol dimethacrylate, 1,2-ethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, and divinyl benzene.
The glass transition temperature (xe2x80x9cTgxe2x80x9d) of the emulsion polymer is from xe2x88x9290xc2x0 C to 20xc2x0 C., as measured by differential scanning calorimetry (DSC) taking the mid-point in the heat flow versus temperature transition as the Tg value, the monomers and amounts of the monomers being selected to achieve the desired polymer Tg range as is well known in the art. Preferred Tg of the emulsion polymer for elastomeric wall coatings is from xe2x88x9240xc2x0 C. to 20xc2x0 C. of caulks and sealants is xe2x88x9260xc2x0 C. to 20xc2x0 C.; of pressure sensitive adhesives is xe2x88x9290xc2x0 C. to 0xc2x0 C.
The polymerization techniques used to prepare aqueous emulsion-polymers are well known in the art. In the emulsion polymerization process conventional surfactants may be used such as, for example, anionic and/or nonionic emulsifiers such as, for example, alkali metal or ammonium salts of alkyl, aryl, or alkylaryl sulfates, sulfonates or phosphates; alkyl sulfonic acids; sulfosuccinate salts; fatty acids; ethylenically unsaturated surfactant monomers; and ethoxylated alcohols or phenols. The amount of surfactant used is usually 0.1% to 6% by weight, based on the weight of monomer. Either thermal or redox initiation processes may be used. The reaction temperature is maintained at a temperature lower than 100xc2x0 C. throughout the course of the reaction. Preferred is a reaction temperature between 30xc2x0 C. and 95xc2x0 C., more preferably between 50xc2x0 C. and 90xc2x0 C. The monomer mixture may be added neat or as an emulsion in water. The monomer mixture may be added in one or more additions or continuously, linearly or not, over the reaction period, or combinations thereof
Conventional free radical initiators may be used such as, for example, hydrogen peroxide, sodium peroxide, potassium peroxide, t-butyl hydroperoxide, cumene hydroperoxide, ammonium and/or alkali metal persulfates, sodium perborate, perphosphoric acid and salts thereof, potassium permanganate, and ammonium or alkali metal salts of peroxydisulfuric acid, typically at a level of 0.01% to 3.0% by weight, based on the weight of total monomer. Redox systems using the same initiators coupled with a suitable reductant such as, for example, sodium sulfoxylate formaldehyde, ascorbic acid, isoascorbic acid, alkali metal and ammonium salts of sulfur-containing acids, such as sodium sulfite, bisulfite, thiosulfate, hydrosulfite, sulfide, hydrosulfide or dithionite, formadinesulfinic acid, hydroxymethanesulfonic acid, acetone bisulfite, amines such as ethanolamine, glycolic acid, glyoxylic acid hydrate, lactic acid, glyceric acid, malic acid, tartaric acid and salts of the preceding acids may be used. Redox reaction catalyzing metal salts of iron, copper, manganese, silver, platinum, vanadium, nickel, chromium, palladium, or cobalt may be used. However, after 90-99.7%, preferably 95-99.7%, of the monomers by weight, based on the total weight of the polymer, have been converted to polymer, at least half of the remaining monomer is converted to polymer in the presence of 0.1-1.0%, by weight based on the total weight of the polymer, of t-amyl hydroperoxide. This part of the reaction may be effected as soon as 90-99.7%, preferably 95-99.7%, conversion of the monomers to polymer is completed in the same reaction vessel or kettle. It may be effected after a period of time, in a different reaction vessel or kettle, or at a different temperature than the preceding part of the polymerization. Preferred is the presence of t-amyl hydroperoxide only after 90%, more preferably after 95%, conversion of the monomers to polymer is completed.
Chain transfer agents such as, for example, halogen compounds such as tetrabromomethane; allyl compounds; or mercaptans such as alkyl thioglycolates, alkyl mercaptoalkanoates, and C4-C22 linear or branched alkyl mercaptans may be used to lower the molecular weight of the formed polymer and/or to provide a different molecular weight distribution than would otherwise have been obtained with any free-radical-generating initiator(s). Linear or branched C4-C22 alkyl mercaptans such as n-dodecyl mercaptan and t-dodecyl mercaptan are preferred. Chain transfer agent(s) may be added in one or more additions or continuously, linearly or not, over most or all of the entire reaction period or during limited portion(s) of the reaction period such as, for example, in the kettle charge and in the reduction of residual monomer stage.
The average particle diameter of the emulsion-polymerized polymer particles is preferred to be from 30 nanometers to 500 nanometers, as measured by a BI-90 Particle Sizer.
The aqueous composition is prepared by techniques which are well known in the coatings art. First, if the elastomeric coating, caulk, sealant or pressure sensitive adhesive composition is to be pigmented, at least one pigment is well dispersed in an aqueous medium under high shear such as is afforded by a COWLES(copyright) mixer or, for more viscous compositions such as caulks and sealants, a high intensity mixer or mill. Then the waterborne polymer is added under lower shear stirring along with other elastomeric coating, caulk, sealant or pressure sensitive adhesive adjuvants as desired. Alternatively, the aqueous emulsion polymer may be included in the pigment dispersion step. The aqueous composition may contain conventional elastomeric coating, caulk, sealant or pressure sensitive adhesive adjuvants such as, for example, tackifiers, pigments, emulsifiers, coalescing agents, buffers, neutralizers, thickeners or rheology modifiers, humectants, wetting agents, biocides, plasticizers, antifoaming agents, colorants, waxes, and anti-oxidants.
The solids content of the aqueous coating composition may be from about 10% to about 85% by volume. The viscosity of the aqueous composition may be from 0.05 to 2000 Pa.s (50 cps to 2,000,000 cps), as measured using a Brookfield viscometer; the viscosities appropriate for different end uses and application methods vary considerably.
The aqueous composition may applied by conventional application methods such as, for example, brushing and spraying methods such as, for example, roll coating, doctor-blade application, printing methods, air-atomized spray, air-assisted spray, airless spray, high volume low pressure spray, air-assisted airless spray, caulk guns, and trowels.
The aqueous composition may be applied to a substrate such as, for example, plastic including sheets and films, wood, metal, previously painted surfaces, cementitious substrates, asphaltic substrates or the like, with or without a prior substrate treatment such as an acid etch or corona discharge or a primer.
The aqueous composition coated on the substrate is typically dried, or allowed to dry, at a temperature from 20xc2x0 C. to 95xc2x0 C.
The following examples are presented to illustrate the invention and the results obtained by the test procedures.
Abbreviations
AA=acrylic acid
BA=butyl acrylate
MMA=methyl methacrylate
AN=acrylonitrile
EHA=2-ethylhexyl acrylate
DI water=deionized water